[doc] Unwanted padding in type declaration

You can see it in this type declaration: https://doc.rust-lang.org/nightly/nightly-rustc/rustc/mir/enum.PlaceBase.html

Screenshot:

<img width="486" alt="Screenshot 2019-05-12 at 14 45 56" src="https://user-images.githubusercontent.com/3050060/57582401-bc1dea80-74c4-11e9-81a0-e9fc8d4fc179.png">
